.checkerboard {
	position: relative;
	border: 2px solid #333;
	background: #ccc;
	margin: 50px auto 20px;
	width: calc(360px + 4px);
	height: calc(360px + 4px);
	font-size: 24px;
}
.p9.checkerboard {
	font-size: 18px;
}
.p4 .checkerboard-row {
	display: flex;
	flex-wrap: nowrap;
	flex-direction: row;
	width: 100%;
	height: 90px;
}
.p6 .checkerboard-row {
	display: flex;
	flex-wrap: nowrap;
	flex-direction: row;
	width: 100%;
	height: 60px;
}
.p9 .checkerboard-row {
	display: flex;
	flex-wrap: nowrap;
	flex-direction: row;
	width: 100%;
	height: 30px;
}
.p4 .checkerboard-block {
	flex: 1;
	display: inline-block;
	width: 90px;
	height: 90px;
	line-height: 90px;
	text-align: center;
	border-right: 1px solid #333;
	border-bottom: 1px solid #333;
	cursor: pointer;
	user-select: none;
}
.p6 .checkerboard-block {
	flex: 1;
	display: inline-block;
	width: 60px;
	height: 60px;
	line-height: 60px;
	text-align: center;
	border-right: 1px solid #333;
	border-bottom: 1px solid #333;
	cursor: pointer;
	user-select: none;
}
.p9 .checkerboard-block {
	flex: 1;
	display: inline-block;
	width: 30px;
	height: 30px;
	line-height: 30px;
	text-align: center;
	border-right: 1px solid #333;
	border-bottom: 1px solid #333;
	cursor: pointer;
	user-select: none;
}

.checkerboard-block.is-choosed {
	background: skyblue;
}

.checkerboard-block:last-child {
	border-right: none;
}

.p4 .checkerboard-block:nth-child(2n) {
	border-right-width: 2px;
}
.p6 .checkerboard-block:nth-child(3n) {
	border-right-width: 2px;
}
.p9 .checkerboard-block:nth-child(3n) {
	border-right-width: 2px;
}

.multiple-of-three .checkerboard-block {
	border-bottom-width: 2px;
}

.last-row .checkerboard-block {
	border-bottom: none;
}

.is-inited {
	background: #ddd;
	cursor: not-allowed;
}
.p4 .coordinate-row {
	position: absolute;
	left: 0;
	top: -90px;
	width: 360px;
	height: 90px;
}

.p4 .coordinate-col {
	position: absolute;
	top: 0;
	left: -90px;
	height: 360px;
	width: 90px;
}

.p4 .coordinate-block {
	display: inline-block;
	width: 90px;
	height: 90px;
	line-height: 90px;
	text-align: center;
}

.p6 .coordinate-row {
	position: absolute;
	left: 0;
	top: -60px;
	width: 360px;
	height: 60px;
}

.p6 .coordinate-col {
	position: absolute;
	top: 0;
	left: -60px;
	height: 360px;
	width: 60px;
}

.p6 .coordinate-block {
	display: inline-block;
	width: 60px;
	height: 60px;
	line-height: 60px;
	text-align: center;
}
.p9 .coordinate-row {
	position: absolute;
	left: 0;
	top: -40px;
	width: 360px;
	height: 40px;
}

.p9 .coordinate-col {
	position: absolute;
	top: 0;
	left: -40px;
	height: 360px;
	width: 40px;
}

.p9 .coordinate-block {
	display: inline-block;
	width: 40px;
	height: 40px;
	line-height: 40px;
	text-align: center;
}
